1. Field of the Invention
The present invention relates to an angular velocity sensor device for sensing angular velocity for use in cars or other vehicles.
2. Description of the Related Art
FIG. 12 is a perspective view showing a conventional angular velocity sensor device, and FIG. 13 is a cross-sectional view of the device of FIG. 12 taken along a line XIII--XIII.
This angular velocity sensor device comprises a substrate 2 manufactured of an insulating material such as glass and having a rectangular recess 2a in cross section, and a Y-axis angular velocity sensing body 4 provided along the surface of the substrate 2 for sensing angular velocity around a Y axis as the axis of rotation along the surface of the substrate 2.
The Y-axis angular velocity sensing body 4 comprises a generally T-shaped vibrator 9 having a base 7 bonded onto the substrate 2 and a beam 8 that can be deflected and vibrated, first and second X-axis vibration detection electrodes 10 and 11 respectively arranged on both sides of and in parallel with the beam 8, and a Z-axis Coriolis force sensing electrode 3 formed in the recess 2a.
FIG. 14 shows the manufacturing process of the Z-axis Coriolis force sensing electrode 3 formed on the substrate 2, in which the recess 2a is made first by etching glass with hydrofluoric acid or the like as shown in FIG. 14(a). Then, Pt is deposited on the entire top surface of the substrate 2 through a sputtering technique, thereby forming electrode 21 (FIG. 14(b)). Next, resist 22 is applied onto the electrode 21 (FIG. 14(c)). The resist coating 22 is exposed to light under a predetermined mask 23 and developed to strip unwanted portions (FIG. 14(d) and FIG. 14(e)). Unwanted portions of the electrode 21 are removed by an ion beam (FIG. 14(f)), and finally the resist 22 is removed (FIG. 14(g)) to form the Z-axis Coriolis force sensing electrode 3.
The operation of the angular velocity sensor device will now be discussed. When the beam 8 is driven and excited by a source of vibration in the X axis, namely in the transverse direction across the beam 8 along the plane of the substrate 2, the beam 8 vibrates in a simple harmonic mode relative to the base 7. A first gap 13 between the beam 8 and the first X-axis vibration detection electrode 10 and a second gap 14 between the beam 8 and the second X-axis vibration detection electrode 11 vary in their magnitude, and the sensed capacitance of an X-axis vibration detection capacitor 70 composed of the beam 8 and the X-axis vibration detection electrodes 10, 11 changes. Based on the value of the capacitance, the device is regulated so that the beam 8 is put into a predetermined drive/excitement state.
When the sensed capacitance of the X-axis vibration detection capacitor 70 changes, the change in capacitance is monitored as a voltage value through a capacitance-voltage converter circuit. Since voltage change is correlated to capacitance change, and capacitance change in turn is correlated to displacement due to vibration, the displacement due to vibration may be regulated at a constant by regulating the voltage change at a constant. More particularly, control is made such that the amplitude of the voltage value obtained as an output is kept at a constant. In the method of regulating the amplitude of the voltage value to a constant, the waveform of the voltage is half-wave rectified or full-wave rectified, and integrated, and feedback control is made such that the integrated value is kept at a constant. In this way, the amplitude of vibration of the beam 8 is regulated at a predetermined value.
An angular velocity about a Y-axis direction as the axis of rotation, that is, about the longitudinal direction of the beam 8, is applied to the vibrator 9 while the beam 8 vibrates in a simple harmonic mode relative to the base 7 along the plane of the substrate 2, a Coriolis force develops in the Z-axis direction, namely in the direction perpendicular to the substrate 2. As a result, the resultant force from the Coriolis force acting in the Z axis and the driving force acting in the X axis displaces the beam 8 in an elliptical trajectory, and thus the magnitude of a third gap 15 between the beam 8 and the Z-axis Coriolis force sensing electrode 3 varies. This means that the sensed capacitance of a Z-axis Coriolis force sense capacitor 71 created by the beam 8 and the Z-axis Coriolis force sensing electrode 3 also varies. The change in capacitance is output as an output voltage by the capacitance-voltage converter circuit, and the corresponding output signal is fed to a computer unit, and thus the angular velocity about the Y axis, as the axis of rotation is sensed.
In such a conventional angular velocity sensor device, however, the Coriolis force acts in the direction perpendicular to the direction in which the beam 8 is driven, and to sense the position of the beam 8 displaced by Coriolis force, the magnitude of variation in the third gap 15 between the beam 8 and the Z-axis Coriolis force sensing electrode 3 is sensed as the capacitance value of the Z-axis Coriolis force sense capacitor 71. For this reason, the Z-axis Coriolis force sensing electrode 3, which is an element of the Z-axis Coriolis force sense capacitor 71, has to be fabricated in the recess 2a of the substrate 2 of a insulating material as shown in FIG. 14, requiring a complex manufacturing process that pushes up the manufacturing cost.